I have Chitika in my website and based on the reports, I'm having 500 - 800 impressions per day with 0 valid clicks, 0 CTR and 0 CPM.
I am wondering why is my revenue still $0.00 even though I have high impression count?
You have no revenue because you have zero clicks. Like many ad networks, Chitika pays only for valid clicks. They don't pay per impression.
To get revenue, a user that sees the ad has to click on it.
Stephen Ostermiller is correct. But I would like to add this for your understanding.
Clicks on ads depend highly upon the relevance of the ad to the interest of the user. This is a difficult thing to do and has little to do with your site at times but rather the ad network. I do not know Chitika, but it is their job for their advertisers to deliver ads that match the interest of the user. The click through rate (CTR) on ads is a reflection of how well the ad network is delivering ads that are relevant to the users interest which is gauged from two things; the topic of the page, and prior history of the user.
It is not always possible that the ad network will have a users history. This is because the user may not be known to the ad network or that for some technical reason, the users history could not be tracked. If this is the case, then it is incumbent upon the ad network to present ads based upon the content.
Some content topics will have a higher CTR based upon user interest. This is natural and is beyond your control fully. For example, if your topic is how to choose an anti-virus software right for you, then ads for anti-software would have a higher CTR. It makes sense. But if your topic is about philosophy, then ad placement becomes harder for the ad network and the relevance of the ad will suffer. Think about it. What ad would go well with philosophy? Past metrics are used by the ad network to gauge user interest by topic. This might result in assumptions based upon not user history, but users (note the plural use of users meaning many in this case) interest from past performance of other sites, impressions, and CTR. In this case, the ad network may assume that life quality products are more important such as aroma therapy. But your philosophy content is aimed at the college student who is doing research for a paper and has little money. They may not be as likely to click on an ad for aroma therapy.
This is why it is sometimes an important measure to try or use more than one ad network. Each has their own strengths and weaknesses. I do not know ad networks strengths and weaknesses enough to comment here. As well, some chose to take control and offer affiliate network ads where you decide what ads will work best on any particular page or site. This is where you have to know the user you attract. You may already have an idea of who they are likely to be. You will have to experiment if you use affiliate ads. Some will seem like the perfect ad, but not convert to a healthy CTR while other ads will.
In the end, it is a bit of a crap shoot (a dice game primarily based upon the random throw of the dice). You will need to try different things to see what works on your site and what does not. We all have to do this. Just placing ads is not always enough and is often ineffective. You will need to explore. Also note, what works for one site may not work for yours. You can see if you can determine what ad networks and affiliate ads that a successful competitor uses that has already run through the cycle of experiments and copy their strategy. But keep in mind, as you do this, you will also want to tailor your site advertising profile to your specific needs because no two sites are created equally.